Cyclic conjugated polymers have electric conductivity because they have a polymer structure wherein n-conjugated electrons are connected, and further, they are excellent in processability and exhibit relatively high environmental stability and heat stability. On that account, they have been paid attention in recent years as materials capable of being used for electric parts, such as organic thin film solar cells, organic thin film transistors, photoelectric conversion materials, organic EL materials, diodes, triodes, electrooptical displays, reflection films and nonlinear optical materials.
Of the cyclic conjugated polymers, those having been paid attention as particularly promising polymers are polymers having a substituent imparting solubility in solvents, such as a hexyl group, at the position other than the main chain skeleton of the cyclic conjugated polymer. It is known that, for example, poly(3-alkylthiophene) undergoes self-assembly, and it is thought that by virtue of this, high electric charge carrier mobility is attained. It is thought that as the molecular weight distribution of poly(3-substituted thiophene) is narrowed, the molecules can undergo self-assembly with one another on a higher level. When the above electric parts are formed from poly(3-substituted thiophene), the poly(3-substituted thiophene) needs to have a molecular weight of a certain degree, from the viewpoint that the electric parts attain given strength or electric conductivity.
Various synthesis processes for such cyclic conjugated polymers have been proposed. For example, a synthesis process for poly(3-substituted thiophene), which is represented by the following chemical reaction formula, is described in a non patent literature 1.

In this process, LDA for use in the step 1 needs to be formed in advance by allowing n-butyllithium and diisopropylamine to react with each other at −40° C. for 40 minutes. On the other hand, when a monomer (2-bromo-3-hexylthiophene) is added in the step 1, it is necessary to control the temperature to a low temperature of −78° C. in order to selectively abstract a proton at the 5-position in a high conversion ratio and to perform lithiation.
Thereafter, the reaction solution is stirred at −40° C. for 40 minutes, then in the step 2, a magnesium bromide-diethyl ether complex (MgBr2.OEt2) is added at −60° C., and the reaction solution is stirred for 20 minutes and then further stirred at −40° C. for 15 minutes. In the step 3, after Ni(dppp)Cl2 (1,3-bis(diphenylphosphinopropane)nickel(II) chloride) is added to the reaction solution at −5° C., the reaction solution needs to be stirred at room temperature for 12 to 18 hours.
In a patent literature 1, a synthesis process for poly(3-substituted thiophene) having an oxazoline residue at the side chain, which is represented by the following chemical reaction formula, is described. Also in this process, LDA is allowed to react with a thiophene compound dissolved in THF and MgBr2.OEt2 at −98° C.

In the processes described in the non patent literature 1 and the patent literature 1, steps of multi-stages are necessary, and each step needs to be carried out after the temperature is controlled to an extremely low-temperature region, and in the case where this process is applied to industrial production, there is a problem that the degree of difficulty of this process becomes extremely high from the viewpoints of process control and cooling ability of mass production facilities.
In patent literatures 2 and 3, a synthesis process for poly(3-substituted thiophene) improved in the above problems is described. In this process, the number of steps is small as shown in the following chemical reaction formula, the reaction time is about 3 hours, and the reaction temperature is not in the above low-temperature region but is under the THF reflux temperature conditions. That is to say, this process is a synthesis process greatly improved from the viewpoint of industrial production.

As for the polymer obtained in the above synthesis process, however, there is no clear description of a molecular weight and regioregularity, and there are fears of lowering of a molecular weight due to shortening of the reaction time, lowering of regioregularity due to a raise in the reaction temperature, etc. Further, the yield of the desired polymer in this reaction is about 40 to 65%, and when industrial production is supposed, this yield cannot be said to be good at all. In addition, in the case where 2,5-dibromination from 3-substituted thiophene is carried out and then mono-metallization is carried out to finally synthesize a polymer, the dibrominated monomer whose polymer chain both end groups are not taken into account is said to have a low atom efficiency because the process is accompanied by elimination of a bromo group of 2 atoms. Furthermore, methyl bromide and methyl iodide formed as reaction by-products in this reaction are substances having been reported to be mutagenic. On that account, the cost of treatment of the mutagenic substances is high, and in the environmental aspect, this process cannot be said to be preferred as an industrial production process requiring mass productivity of the process.
In non patent literatures 2 and 3, a synthesis process for poly(3-substituted thiophene), which is represented by the following chemical reaction formula, is described.

* In the above chemical reaction formula, NIS is N-iodosuccinimide.
In this process, however, synthesis of a monomer used for the polymerization is carried out by multi-stage reaction, as shown in the above formula, and therefore, purification, etc. become necessary in each step (particularly, reaction in the monomer synthesis stage). On that account, when this process is applied to the industrial production of poly(3-substituted thiophene), there is a fear of complicated steps.
In a patent literature 4 and a nonpatent literature 4, a synthesis process for poly(3-substituted thiophene), which is represented by the following chemical reaction formula, is described.

* In the above chemical reaction formula, NBS is N-bromosuccinimide.
In this process, however, the synthesis reaction for a monomer used for the polymerization is a multi-stage reaction, similarly to the process described in the above non patent literatures 2 and 3, and therefore, purification, etc. become necessary in each step (particularly, reaction in the monomer synthesis stage). Hence, when this process is applied to the industrial production, there is a fear of complicated steps.
In a non patent literature 5, a process for obtaining poly(3-hexylthiophene) by polymerizing 2-bromo-3-hexylthiophene in the presence of a palladium catalyst, a specific phosphine compound, cesium carbonate and THF is described.
As shown in the above examples of thiophene, the hitherto known polymerization processes for cyclic conjugated polymers have various problems such that the degree of difficulty of the reaction is high and the treatment of the by-products is complicated.